Document how to use agentk with KAS behind self-signed CA cert

Timo Furrerrequested to merge
master-patch-0d4d into master

What does this MR do and why?

This change set documents how to use agentk with a KAS installation that is behind a self-signed certificate.

Refs Improve communication regarding how to install ... (gitlab-org/charts/gitlab#3839 - closed)

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